Author Archives: admin

Who Are You? (Who, who, who, who)

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Finding DNA

 

Technicians painstakingly extract DNA from a few cells recovered from a crime scene. They duplicate segments of the DNA using the polymerase chain reaction. After analyzing the selected DNA fragments, they upload the results into the FBI’s national DNA database, the Combined DNA Index System (CODIS) Program. The result: No hits. The DNA profile is not in the database. Now what?

Researchers at Israel’s Tel-Hai Academic College may provide an answer with a DNA composite portrait based on connections between genes and external human traits.

“The new development will provide tons of leads,” research team leader Dani Bercovich told news website NoCamels.com. “We’ll know the sex of the offender and be able to estimate his height, age range, color and type of hair, eye color and ethnic background — even whether he is right or left-handed.”

Regardless of whether this technology is realized, it certainly can find a place in a mystery or crime story.

FBI and DOJ Consider Errors in Forensic Evidence

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Questioning forensics

Questioning forensics

 

In the last posting, we saw how an error in DNA analysis can muddy a criminal investigation. But, forensic errors can yield graver consequences, such as a wrongful conviction.

During April 2012, The Washington Post reported that Justice Department officials had known for years about flawed forensic work that might have led to the convictions of potentially innocent people, and that the DOJ had not performed a thorough review of the cases. The Post declared that hair and fiber analyses were subjective and lacked grounding in solid research, and that examiners overstated the significance of a match.

On July 13, the newspaper announced that the DOJ and the FBI launched a review of thousands of criminal cases. The objective is to decide if any defendants were wrongly convicted because of flawed forensic evidence.

The FBI’s post-conviction review will include cases with forensics performed by all FBI Laboratory hair and fiber examiners since at least 1985. These examinations were conducted for both federal and local investigations.

The Washington Post’s story, “Justice Dept., FBI to review use of forensic evidence in thousands of cases,” includes links to articles about the reliability of various types of forensic analysis.

Lab Error Might Have Created False Breakthrough

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DNA molecule unwinding from a chromosome inside the nucleus of a cell. Source: National Human Genome Research Institute.

DNA molecule unwinding from a chromosome inside the nucleus of a cell. Source: National Human Genome Research Institute.

 

On July 10, 2012, The New York Times reported a match between DNA linked to the unsolved 2004 murder of Sarah Fox, a Juilliard student, and DNA recovered from a chain at the site of an Occupy Wall Street protest last March.

Protestors had wrapped the chain around an emergency exit door at a subway station to allow passengers to ride free. A surveillance video revealed people handling the chain, but they wore dark hoods and masks. To find the perpetrators, city officials decided to recover DNA from the chain. That’s when they discovered a match between DNA on the chain and DNA recovered from Sarah Fox’s CD player, which was found near her body.

The news reflects the ability of investigators to extract DNA from skin cells left on doorknobs and other surfaces. These samples are known as “touch DNA.” Recovered weapons are also swabbed for later DNA analysis.

Several surprises quickly followed the news about the DNA match. During the investigation of the 2004 murder, police and the Manhattan district attorney’s office had focused on a construction worker as the primary suspect. They never did find sufficient evidence to charge him. Now, the city reported that the matching DNA does not belong to the prime suspect.

On July 11, The New York Times announced an unexpected development: The DNA match may be due to a lab error. According to an unnamed source, the DNA recovered from skin cells on the student’s CD player and from the chain belong to a Police Department employee who works with the Office of the Chief Medical Examiner.

DNA errors wreak havoc on a criminal investigation. Mystery writers know that the same types of mistakes provide useful plot twists.

A Real Forensic Scientist

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How to contaminate evidence

How to contaminate evidence: No coveralls, no gloves, no booties, and no sense.

 

The website of the Toronto Star has interesting profile of Christine McCarthy, a forensic scientist at Toronto’s Centre for Forensic Sciences. In the July 13, 2012, posting entitled “Hair: Forensic scientists can tell a lot about a person from one strand of hair,” reporter Tony Wong describes McCarthy at work.

In the field, she dons a disposable lab coat, mask, gloves, and a hairnet before she starts her search for trace evidence. This is a very different approach than that used by crime scene technicians on television. Wong compared McCarthy to CSI’s Catherine Willows. “Except I wouldn’t have a Hummer or wear high heels on the job,” McCarthy told him.

She mentioned another of the many differences between CSI characters and her colleagues at the Centre for Forensic Sciences. “They seem to solve everything in an hour,” McCarthy said, “and I can tell you it takes a lot longer than that.”

McCarthy specializes in the analysis of trace evidence, especially hair. Wong’s article offers an overview about this aspect of forensic science.